Moment redistribution in two-span prestressed NSC and HSC beams

Abstract

This paper presents a numerical investigation into two-span continuous prestressed normal-strength concrete (NSC) and high-strength concrete (HSC) beams, focusing on aspects of behavior related to moment redistribution. A comparative study is performed by using an experimentally validated computer model. The concrete cylinder compressive strength of investigated beams covers from 40 to 90 MPa, while the prestressing reinforcement ratio (ρ p) ranges from 0.15 to 1.29%. The results show that the tendon tensile strength can be better exploited by HSC than by NSC at moderate to high ρ p levels. At a given level of ρ p, HSC generally mobilizes smaller neutral axis depth, higher strain in nonprestressed steel and a bit larger moment redistribution at ultimate than NSC. Typical code recommendations (ACI, CSA and EC2) for permissible moment redistribution are examined. The effect of concrete strength on moment redistribution in prestressed beams is well reflected in ACI but inadequately reflected in CSA and EC2. A simplified equation for calculating moment redistribution in continuous prestressed beams is proposed.